In our lives, electronic devices are being used in various fields. These electronic devices have been made lightweight and miniaturized by the development of semiconductors using silicon. However, such silicon (Si)-based semiconductor devices have a small band gap so that those are difficult to apply to high power devices.
To solve the above problem, an electronic device based on gallium nitride (GaN) has been developed. GaN-based electronic devices commonly used for high-power and high-speed electronic devices adopt a sapphire substrate or a silicon carbide substrate. A lattice mismatch between GaN/AlGaN layer and a substrate is high, and high internal fields are induced between an interface the GaN/AlGaN or AlGaN/InGaN/GaN, which is used as an active layer, due to piezoelectric field and spontaneous polarization so that there is an advantage of resulting in a significant decrease in the mobility of the charge [T.-H. Yu and K. F. Brennan, J. Appl. Phys. 89, 382 (2001)].
This is because the mobility at room temperature is mainly determined by polar-optical-phonon scattering, and the scattering rate increases as the electric field applied perpendicularly to the active layer increases, which has been found by the present inventor theoretically, [D. Ahn, “Electric field dependence of intrasubband polar-optical phonon scattering in a quantum well”, Phys. Rev. B 37, 2529 (1988)]. Further, other studies have also shown that spontaneous polarization on the surface also reduces mobility. [Y. Zhang and J. Singh, “Charge control and mobility studies for AlGaN/GaN high electron mobility transistor”, Appl. Phys. 85, 587 (1999)].
However, there is a problem that such a GaN-based semiconductor adopts a sapphire substrate or a silicon carbide substrate so that manufacturing cost becomes expensive. Furthermore, the size of the sapphire substrate or the silicon carbide substrate is not large, so that the number of electronic devices that can be grown on the substrate is also small, resulting in low productivity.